Erosive cutting machine for the final machining of punching and cutting tools

ABSTRACT

Erosive working machine for cutting prepared closed inner shapes (15) and closed outer shapes (16) of a workpiece (12) fixed by a workpiece holder by means of a filamentary or strip electrode (14) arranged on guidance means (13, 18). At least one guidance means (13, 18) is arranged on a motor-rotatable rotating mechanism (20) in such a way that the center line (23) of rotating mechanism (20) at at least one geometrical locus coincides with the center of the cross-section of electrode (14). Thus, during the erosion process, a collision between the guidance means (13, 18) and the closed inner shape (15) or closed outer shape (16) or a tool holder (11) is avoided.

The invention relates to an erosive cutting machine for the finalmachining of prepared closed inner shapes and closed outer shapes of aworkpiece fixed by a workpiece holder by means of a filamentary or stripelectrode arranged on guidance means.

BACKGROUND

Closed workpieces, e.g. punching or cutting tools have in many cases thefeature that the contour to be cut with the electrode is not reachablefrom the outside, because the workpiece walls block access of theelectrode and the guide means carrying the electrode. FIG. 1a shows sucha cutting tool. The spatial dimensions are length 3 m, width 2 m andheight 1.5 m. Such a cutting tool is used for cutting sheet metal partssuch as e.g. automobile bodies after thay have been shaped. As is shown,after shaping, said sheet metal parts have material projecting beyondthe shape limits. This material must be cut off by the cutting toolshown in FIG. 1a. The manufacture of such a cutting tool is verycomplicated, because the contour to be cut out represents a closed innershape. An erosion machine can only cut this contour if the wire guide isparticularly long. However, this means a considerable vibration of theelectrode during the erosion process. Thus, the requisite precisionwould not be maintained. The cutting tool can obviously have smallerspatial dimensions than those of FIG. 1a. In the case of a smaller tool,an erosive cutting machine could not cut the closed inner shape, evenwith lengthened wheel guidance means. FIG. 1b shows a punch having aclosed outer shape and can either be a blanking punch or a cuttingpunch. The external dimensions of the punch can be up to a few meters.The closed outer shape of the punch cannot be machined in one operationwith the known working methods, because it is fixed in a clamping systemand the working machine, e.g. the erosive cutting machine, would collidewith the clamping system. To avoid such a collision, the closed outershape can only be machined in parts. The punch must then be reclamped inthe clamping system and the new alignment then takes place between punchand erosive electrode. As a result of these difficulties, manufacture ofsuch cutting and punching tools has taken a considerable time and isvery complicated, which leads to high costs.

THE INVENTION

The problem of the invention is to obviate these difficulties ordisadvantages occurring in the manufacture of special tools. Theinvention also aims at transferring the advantages of erosive machiningby means of a filamentary or strip electrode to the present specificallyshaped workpieces. The invention also aims at attaining theaformentioned advantages by means of a simple constructional solution,so that one of the constructional embodiments according to the inventioncan be installed on existing erosion machines.

According to the invention this problem is solved in that for avoiding acollision between the guidance means and the closed inner shape or theclosed outer shape and the workpiece holder at least one guidance meansis provided on the motor-rotatable rotating mechanism, whose centre linecoincides at at least one geometrical locus with the centre of thecross-section of the electrode.

Important features of the constructions according to the invention canbe gathered from the claims.

DRAWINGS:

The figures show FIG. 1a and 1b are punch elements to be made by themachine apparatus;

FIG. 2 an embodiment of the invention where, as desired, one or twoguidance means for the electrode are provided on a rotating mechanism.

FIG. 3a the cutting of a workpiece with closed outer shape.

FIG. 3b the cutting of a workpiece with a closed inner shape.

FIG. 4 a further embodiment of the invention with sensors on theguidance means.

FIG. 5 an elecrode arrangement according to the invention to and fromthe guidance means in a sectional view along the section line A--A ofFIG. 2.

FIG. 6 a part sectional representation of an electrode supply anddischarge arrangement according to the invention.

FIG. 2 is a part sectional representation of the machining head of anerosive cutting machine. Such a machining head with the guidanceelements for the filamentary or strip electrode can be constructed inthe manner described in U.S. Pat. No. 3,891,819, U.S. Pat. No. 3,928,163and U.S. Pat. No. 3,987,270 . According to FIG. 2, the working headwhich is fixed to the not shown erosion machine carries the rotatingmechanism 20 in a special recess. This rotating mechanism isdisplaceably arranged in the working or machining head 1 by means ofbearing 191. The drive motor 192 moves the spindle 61 in such a way thatthe entire rotating mechanism 20 can be moved upwards or downwards. Theelectrical terminals are symbolically shown in motor 192, which can beoperated by a not shown electrical control mechanism. The rotatingmechanism 20 comprises a fixed structural member 19 and the rotarystructural member 17, the latter being rotatably mounted in the fixedstructural member 19 in bearing 171. Rotation is effected by motor 172connected to a not shown electrical control circuit by means of theindicated terminals. Pinion 173 moves the toothed belts 174 engaging incorresponding mating teeth of the rotating structural member 17, so thatthe latter can be rotated at random either to the right or to the left.A brake 175 is provided which stops the rotary structural member 17 inthe desired position. The rotary structural member 17 has a cross-table42 at the lower end. The upper table can move in direction P and thelower table in direction Q. The two directions are indicated by arrowsin FIG. 2 and are displaced by 90° from one another. On cross-table 42is provided the support structure 21, which carries the rollers 71 forthe filamentary or strip electrode 14. The special features of saidrollers 47 are described in conjunction with FIG. 5. Electrode 14 isconveyed from the supply side, which in FIG. 2 is shown as a deliveryspool 72, via guide rollers or pulleys 71, 73 to the guidance means 13,18 between which the work zone 1318 is located; and from there to thedischarge side 81. During the erosive machining process, electrode 14moves at a constant speed from the supply side 72 to the discharge side81. The guidance means 13, 18, which are only symbolically shown and inreality are constructed in the manner described and shown in theaforementioned U.S. Patents, are fixed to guidance means supports 122a,122b. One guidance means 13 is arranged with its support 122b on across-slide 41, which can be moved in direction V and direction U. Thismovement is indicated by respective arrows in FIG. 2. Reference numerals101 and 121 indicate a rotary table and a spacer, which will bedescribed in greater detail hereinafter. Cross-table 42 is fixed to amovement member 25, comprising a sleeve and a spindle. The spindle ismoved in one or other direction by motor 23. This movement leads to adisplacement of cross-slide 42, arm 122 b and guidance means 13 indirection Z1. This direction, either upwards or downwards is indicatedby arrows. Motor 23 is correspondingly controlled by means of terminalsfrom a not shown electrical circuit arrangement and is fixed to thesupport structure 21. In a special manner, support structure 21 caneither be connected to the fixed part 19 or indirectly with cross slide42 of rotating mechanism 20. This will be described in greater detailhereinafter. Connecting means 211 and 212, which can be constructed asclamping, screw or plug connections, constitute the connection eitherwith part 19 or cross slide 42 of the rotating mechanism in such a waythat in each case one of the two connecting means forms the connectionand the other is free. If e.g. connecting means 211 connects supportstructure 21 to the fixed part 19 of rotating mechanism 20, the otherconnecting means 212 must interrupt the connection between supportstructure 21 and cross-slide 42. If support structure 21 is fixed tocross-slide 42, connecting means 212 must provide the connection andconnecting means 211 must interrupt the connection between rotatingmechanism 20 and fixed part 19. If the support structure 21 is connectedto the cross-slide 42 or support structure 26, both arms 122a, 122b orguidance means 13, 18 are jointly moved with the rotating mechanism 20.If the support structure is connected to the fixed part 19, the rotarypart 17 of rotating mechanism 20 now only rotates arm 122 with guidancemeans 18 in one or other direction. In this case, the other guidancemeans 13 connected with arm 122b does not rotate. These twoalternatives, that is, joint rotation of the two guidance means 13, 18or rotation of only one guidance means 18) will be described in greaterdetail hereinafter in conjunction with the various working methods. FIG.2 is a sectional view of the cutting tool of FIG. 1a. By means of theembodiments of FIGS. 2, 3b and 4 and 6, the cut surface 15 is to beworked by means of electrode 14. It is assumed that the tool of FIG. 1ahas already been roughly machined. Electrode 14 now serves to producethe final cut surface 15. The cutting tool 12 of FIG. 1a is called theworkpiece 12 in the following description of FIGS. 2, 3b, and 4 and 6.

According to FIG. 2, the cut surface 15 of workpiece 12 is machined byintroducing the lower arm 122 with guidance means 18 into the opening ofworkpiece 12. Wire electrode 14 has already been supplied from thesupply side 72 via the various guide pulleys 71 and 73 to the guidancemeans 18, 13 and then to the discharge side 81. Hereinafter, afilamentary electrode is used for machinging purposes, so that the termwire electrode is often employed. It is assumed that the supportstructure 21 to which is fixed the upper arm with the guidance means 13is secured by connecting means 212 to structural member 26. Prior to thestart of the actual erosive cutting of the surface 15 of workpiece 12,it is necessary to align the wire electrode 14. This is done by movingcross-slide 41 in directions U and/or V until wire electrode 14 iscoaxial to the centre line 23 of rotating mechanism 20. During thiscoaxial positioning, wire electrode 14 is located somewhere within theopening defined by the cut surface 15 of workpiece 12. It is essentialfor the wire electrode to be parallel to the centre line 23. In the nextstate, cross-slide 42 is moved in directions P and Q until the wireelectrode 14 between the two guidance means 13 and 18 is accuratelycentered with the centre line 23 or with the rotation axis 24 ofrotating mechanism 20. As in this case support structure 21 is connectedto structural member 26 and therefore also to the lower arm 122 ofguidance means 18, the two guidance means move together with thecross-slide 42. This means that the parallel position of wire electrode14 with respect to the centre line 20 is not changed by the movement ofcross-slide 42. If wire electrode 14 coincides with centre line 23, thearms 122a, 122b of the two guidance means 13 and 18 are adjusted in sucha way that the arms 122a, 122b are precisely at a right angle to the cutsurface 15 of workpiece 12. During the erosive machining of cut surface15, the entire machining head 1 of FIG. 2 is moved in the way it iscontrolled by an electronic control system. Such electronic controlsystems are adequately known and will not be described in detail here.Electronic control systems are for example described in U.S. Pat. No.3,859,186, U.S. Pat. No. 3,873,102, U.S. Pat. No. 3,975,607 and U.S.Pat. No. 4,045,641. When machining the cut surface 15 of workpiece 12,it is ensured that the arms are always at a right angle to the cutsurface. The distance between the two guidance means 13 and 18 is calledthe spacing and should be kept as small as possible, so that the wireelectrode 14 does not vibrate unnecessarily during erosive machining. Itis therefore frequently necessary for the two guidance means to followthe three-dimensional shape of the cut surface 15 without varying thespacing. This is brought about in that the motor 192 of FIG. 2 can movethe entire rotating mechanism including fixed part 19, 20 upwards ordownwards by means of spindle 61. Account can also be taken of theso-called "topography" of the workpiece 12 through the motor 27 movingupwards or downwards the upper arm 122b of guidance means 13. However,it must be borne in mind that the spacing between the two guidance means13 and 18 changes. The spacing must not be increased to such an extentthat electrode 14 vibrates during the erosion process. Throughout theerosion process, electrode 14 is always to be held in the rotation axis24 or in the wire centre line 23. This ensures that the remainscorrectly adjusted against workpiece 12 if rotary part 17 is rotated.This condition must also be fulfilled in the case of conical cutting.Conical cutting is understood to mean that the electrode 14 fixedbetween the guidance means 13 and 18 assumes a specific angle relativeto the cutting surface of workpiece 12. Due to this conical cutting,there is an angle of slope of the cut surface 15. The angular setting ofelectrode 14 is brought about in that the cross-table 42 is moved indirections U and/or V until the electrode 14 assumes the desired angle.In this case, electrode 14 is positioned between guidance means 13 and18 in such a way that it is no longer parallel or coaxial to the centreline 24.

For conical cutting, only one point of the wire electrode must be crosswith the center line 24, instead of the total wire line as it has beenthe case so far. The crossing point should be located anywhere betweenguidance means 13 and 18. The crossing point is a reference for a conewhich is wanted as a special workpiece cutting figure. According to thecone angle and the distance to said reference point, the position of theguidance means 18 must be adjusted using slide table 42 for P and Q. Theposition of the upper guidance means 13 will then be controlleddepending upon the position of the lower guidance means 18, by drivingmeans for U, V at the cross-table 41.

For reasons of completeness, it is pointed out that the spacing betweenthe guidance means 13 and 18 can be varied by spacers and, according toFIG. 2, they are provided in arm 122a, 122b. The arrangement of one ormore spacers in one or several arms 122a, 122b can be achieved withoutdifficulty. It is dependent on the particular machining case. Suchspacers are generally known, as is their fixing.

FIG. 3a shows punch 12 of FIG. 1b in a sectional view. The punch is alsofixed to the table 11. The wire electrode 14 cuts the closed outer shape16 on punch 12. In the manner described relative to FIG. 2, electrode 14can cut the outer shape 16 cylindrically (as shown in FIG. 3a) orconically. The movement possibilities of arms 122 of the two guidancemeans 13, 18 are present in the same way as described hereinbefore. Theyare not impeded by any clamping means fixing punch 12 to table 11. Forreasons of completeness, it is pointed out that in FIG. 3a upper arm 122with guidance means 13 contains no rotary table 101 and no spacer 121.This indicates that members 101 and 121 can only be used in specialcases, such as e.g. in FIG. 2.

FIG. 3b shows a similar sectional representation to the lower part ofFIG. 2, whereby in FIG. 1a, the workpiece 12 is shown in perspective.FIG. 3b is intended to show that for any "topography" of workpiece 12,the two arms 122 of guidance means 13, 18 with an identical spacing(i.e. the reciporcal spacing of the guidance means) can carry out theerosion. This is carried out in that according to FIG. 2 only motor 192and not motor 23 is operated. Wire electrode 14 has an unimpededaccessibility to the different cutting lines 15, which are not conicalin FIG. 3b.

FIG. 4 shows a further embodiment whereby sensors 31 are provided on thearms 122 of guidance means 13, 18. These sensors are known per se andare fitted to the arms as shown in FIG. 4. The sensor on upper arm 132(guidance means 13) produces a corresponding signal if it comes intocontact with the surface of workpiece 12. A plurality of sensors 31 arearranged in various ways on lower arm 122 (guidance means 18). Thesesensors serve to prevent a collision with the inner walls of workpiece12. When they come into contact with one of these surfaces they producean electrical signal. The electrical signals of sensors 31 reach thecontrol system and starts up the corresponding movement of motors 192,23 or 172 (FIG. 2). Motor 192 is used for moving the two guidance means13, 18, as indicated in FIG. 2 with Z2. Motor 23 is used for moving theupper guidance means 13, indicated in FIGS. 2 and 4 with Z1. Motor 172is used for rotating rotating mechanism 20 and according to FIGS. 2 and4 this is carried out by means of drive 173, 174. Unlike in FIG. 2, inFIG. 4 the support structure 21 is permanently fixed to structuralmember 26. This is intended to show that fixing means 211 and 212 ofFIG. 2 are not necessary in all cases. Motor 23 is fixed to supportstructure 21 and operates the upper arm 122 of guidance means 13 indirection Z1. Support structure 21 is connected to the structural member26 and not to the fixed part 19 of the rotating mechanism. Thus, in thiscase, the two arms 122 move if by means of spindle 61 (FIG. 2) motor 192moves the complete rotating mechanism upwards or downwards in directionZ2. In FIG. 2, the same members as in FIG. 2 are given the samereference numerals and are not mentioned again.

FIG. 5 shows a section along the lines A-A of FIG. 2. The viewingdirection is indicated by arrows, i.e. it is from bottom to top in FIG.2. FIG. 5 shows the wire electrode which, from the supply side, passesover pulleys 73 and 71. The first pair of pulleys is located on thefixed part of the rotating mechanism. The following pair of pulleys 71is located, like the individual pulleys 71 on structural member 26which, with the rotary parts 17 of rotating mechanism 20, can be rotatedinto any random position. The lower arm 122 of guidance means 18 isshown in sectioned form, whereas the upper arm 122 with guidance means13 is not sectioned. According to FIG. 5, wire electrode 14 passes fromthe second pair of pulleys 71 to the pulley of lower arm 122 and isguided by guidance means 18. From there, it passes from the guidancemeans 13 of upper arm 122 and then onto the discharge side 81. Wireelectrode 14 is precisely positioned on the centre line 23 of rotatingmechanism 20. It is assumed that during the erosion process, cuttingline 15 or 16 of workpiece 12 requires a rotation of rotating mechanism20. This takes place by controlling motor 172 which, by means of toothedgear 173 and toothed belt 174 correspondingly rotates the rotary part 17of the rotating mechanism. For illustration purposes, it is assumed thatrotary parts 17 and consequently also structural member 26, togetherwith arms 122 are rotated in the clockwise direction. As the supply side72 of wire electrode 14, as well as pulley 73 and the first pair ofpulleys 71 remain at the same place, guide pulley 71, which in FIG. 5 ispositioned below the sectioned arm 122, takes over the further guidanceof wire electrode 14 to the second pair of pulleys 71 and onto the arms122. If during the erosion process, rotating mechanism 20 must rotatefurther to the right, the next pulley 71, located at the right handbottom side of FIG. 5, takes over the guidance of wire electrode 14 fromthe supply side. If the wire electrode discharge side is provided in themanner shown in FIG. 2, i.e. if electrode 14 is on the centre line 23 ofrotating mechanism 20, said discharge side 81 requires no special guidepulleys, as indicated e.g. in FIG. 5 for the supply side. However, ifthe discharge side 81 of wire electrode 40 is constructed in such a waythat it is no longer located on the centre line 23 of rotating mechanism20, it is also necessary to provide a device of the type shown in FIG. 5for the discharge side.

If the supply side 72 for wire electrode 14 can be positioned on centreline 23 or in the vicinity thereof, then the device of FIG. 5 is nolonger required for the supply side. The same also applies if supplyside 72 and discharge side 81 are located on the rotating mechanism 20.In this case, the relative position of supply side and discharge side toguidance means 13, 18 remains constant. In this case, a device accordingto FIG. 5 would not be necessary.

FIG. 6 shows an embodiment in which the supply side 72 and dischargeside 81 of wire electrode 3 are located as close as possible to thecentre line 23 of the rotating mechanism. Such an arrangement is readilypossible due to corresponding guide pulleys positioned on fixed part 19of rotating mechanism 20. It is immediately apparent that the supply anddischarge sides of the wire electrode can be positioned on the rotarymember 17, e.g. on structural member 26. FIG. 6 will not be discussed indetail because the structural members are the same as in FIGS. 2, 3 and4 and therefore have the same reference numerals.

I claim:
 1. Erosive cutting machine for the final machining of preparedclosed inner shapes and closed outer shapes of a workpiece (12) havingaworkpiece holder (11) to retain the workpiece; a filamentary or stripelectrode (14); and guidance means, including upper and lower guideelements (13, 18), for guiding the electrode through a working orcutting zone (1318) comprising a motor rotatable rotary mechanism (20)having an axis of rotation (24) which has a common reference point onthe axis (23) of the electrode (14); a first cross slide (41) which iscontrollably driven for controlling any desired cutting cone and whichcarries an upper arm (122b); a second cross slide (42) which iscontrollably driven and positioning the wire guidance means (13, 18) onsaid reference point; and means (27) for continuous adjustment (Z1) ofthe distance between the upper and lower guidance elements (13, 18). 2.Machine according to claim 1, wherein, for cutting of shapes of circularoutline, the rotating mechanism (20) has an axis of rotation (24) whichcoincides with the axis (23) of the electrode (14) on at least one pointwithin the working or cutting zone (1318).
 3. Machine according to claim1, including means (192) for controlled vertical adjustment of therotary mechanism (20) to adjust the location of the cutting zone (1318)according to the requirements of the workpiece (12).
 4. Machineaccording to claim 1, wherein the first cross slide (41) includesvertical guidance means (Z1);and connecting means (211, 212) forconnecting the vertical guidance means (Z1) of the first cross slide(41) selectively (a) with the second cross slide (42), or (b) with thefixed part (19) of the rotary mechanism (20).
 5. Machine according toclaim 1, wherein the first cross slide (41) positions the axis (23) ofthe electrode (14) coaxially with the axis of rotation (24) of therotary mechanism (20);and the second cross slide (42) positions theguidance means (18) for centering the axis (23) of the electrode (14) onsaid axis of rotation (24) of the rotary mechanism.
 6. Machine accordingto claim 1 or 2, wherein both the first and second guidance elements arefixed to a rotary part (17) of the rotary mechanism (20).
 7. Machineaccording to claim 1 or 5, wherein one guidance element (13) is fixed toa fixed part (19) of the rotary mechanism and the other guidance element(18) is fixed to a rotary part (17) of the rotary mechanism.
 8. Machineaccording to claim 1, wherein the rotary mechanism (20) comprisesasupport (21) for supporting one (13) of the guidance elements; andattachment means (211, 212) for the selective attachment of the supportto a rotary part (17) or to a fixed part (19) of the rotary mechanism(20).
 9. Machine according to claim 1, wherein at least one guidanceelement (13) is secured to one (41) of the cross slides (41, 42) forsetting a particular angle of the electrode (14) with respect to asurface of the workpiece (12).
 10. Machine according to claim 1,including a translating mechanism (61);and wherein both guidanceelements (13, 18) are located on a translating mechanism for translationof both guidance elements at a constant spacing.
 11. Machine accordingto claim 10, wherein the translating mechanism (61) includes means fortranslation and process-controlled displacement of both guidanceelements, while maintaining constant spacing with respect to oneanother, and further maintaining the angular relative position betweenthe electrode wire (14) and a surface of the workpiece (12).
 12. Machineaccording to claim 1, including at least one collision detector (41)coupled to the guidance means (13, 18) for detecting collision betweenthe guidance means and an inner or outer surface of the workpiece (12).13. Machine according to claim 1, wherein the rotary mechanism (20)comprises a rotary part (17) including a structural member (26);pulleys(71) are provided, uniformly arranged over the periphery of thestructural member; and a reeling means (72, 81) is provided for supplyand removal of the electrode (14) to and from the work zone (1318), thepulleys guiding the electrode between the guidance means (13, 18) andsaid reeling means (72, 81).
 14. Machine according to claim 13, whereinthe reeling means (72, 81) are secured to the rotary mechanism (20) andperform rotary movement therewith so that, upon operation of the rotarymechanism, the relative position of the reeling means with respect tothe guidance means remains unchanged.
 15. Machine according to claim 13,wherein the reeling means (72, 81) is positioned close to the axis ofrotation (24) of the rotary mechanism (20) and spaced from said axis bya distance in which, upon operation of the rotary mechanism, thevariation in the relative position of the reeling means with respect tothe guidance means does not exceed a predetermined value.
 16. Machineaccording to claim 1, wherein the cross slides (41, 42) operate in aCartesian system of coordinates;and a rotary table (101) operating in apolar system of coordinates is provided, coupled to one (13) of theguidance elements to provide for conical cuts on the workpiece by theelectrode (14).
 17. Machine according to claim 1, includinginterchangeable spacing means positioning at least one (13) of saidguidance elements for changing the distance between said elements.